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(#) StateFlow.value should not be called within composition

!!! ERROR: StateFlow.value should not be called within composition
   This is an error.

Id
:   `StateFlowValueCalledInComposition`
Summary
:   StateFlow.value should not be called within composition
Severity
:   Error
Category
:   Correctness
Platform
:   Any
Vendor
:   Jetpack Compose
Identifier
:   androidx.compose.runtime
Feedback
:   https://issuetracker.google.com/issues/new?component=612128
Min
:   Lint 8.0 and 8.1
Compiled
:   Lint 8.0 and 8.1
Artifact
:   [androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html)
Since
:   1.5.0
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/main/java/androidx/compose/runtime/lint/ComposableStateFlowValueDetector.kt)
Tests
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/ComposableStateFlowValueDetectorTest.kt)
Copyright Year
:   2021

Calling StateFlow.value within composition will not observe changes to
the StateFlow, so changes might not be reflected within the composition.
Instead you should use stateFlow.collectAsState() to observe changes to
the StateFlow, and recompose when it changes.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/androidx/compose/runtime/foo/TestFlow.kt:20:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:24:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:25:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:29:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:30:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:39:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:40:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:43:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:44:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:50:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:51:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
src/androidx/compose/runtime/foo/TestFlow.kt:55:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    stateFlow.value
              -----
src/androidx/compose/runtime/foo/TestFlow.kt:56:Error: StateFlow.value
should not be called within composition
[StateFlowValueCalledInComposition]
    testFlow.value
             -----
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/androidx/compose/runtime/foo/TestFlow.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package androidx.compose.runtime.foo

import androidx.compose.runtime.Composable
import kotlinx.coroutines.flow.*

val stateFlow: StateFlow<Boolean> = object : StateFlow<Boolean> {
    override val value = true
}

class TestFlow : StateFlow<Boolean> {
    override val value = true
}

val testFlow = TestFlow()

@Composable
fun Test() {
    stateFlow.value
    testFlow.value
}

val lambda = @Composable {
    stateFlow.value
    testFlow.value
}

val lambda2: @Composable () -> Unit = {
    stateFlow.value
    testFlow.value
}

@Composable
fun LambdaParameter(content: @Composable () -> Unit) {}

@Composable
fun Test2() {
    LambdaParameter(content = {
        stateFlow.value
        testFlow.value
    })
    LambdaParameter {
        stateFlow.value
        testFlow.value
    }
}

fun test3() {
    val localLambda1 = @Composable {
        stateFlow.value
        testFlow.value
    }

    val localLambda2: @Composable () -> Unit = {
        stateFlow.value
        testFlow.value
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/ComposableStateFlowValueDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `ComposableStateFlowValueDetector.errors`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=612128.

(##) Including

!!!
   This is not a built-in check. To include it, add the below dependency
   to your project.

```
// build.gradle.kts
implementation("androidx.compose.runtime:runtime-android:1.8.0-alpha07")

// build.gradle
implementation 'androidx.compose.runtime:runtime-android:1.8.0-alpha07'

// build.gradle.kts with version catalogs:
implementation(libs.runtime.android)

# libs.versions.toml
[versions]
runtime-android = "1.8.0-alpha07"
[libraries]
# For clarity and text wrapping purposes the following declaration is
# shown split up across lines, but in TOML it needs to be on a single
# line (see https://github.com/toml-lang/toml/issues/516) so adjust
# when pasting into libs.versions.toml:
runtime-android = {
    module = "androidx.compose.runtime:runtime-android",
    version.ref = "runtime-android"
}
```

1.8.0-alpha07 is the version this documentation was generated from;
there may be newer versions available.

NOTE: These lint checks are **also** made available separate from the main library.
You can also use `androidx.compose.runtime:runtime-lint:1.8.0-alpha07`.


[Additional details about androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html).
(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("StateFlowValueCalledInComposition")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("StateFlowValueCalledInComposition")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection StateFlowValueCalledInComposition
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="StateFlowValueCalledInComposition" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'StateFlowValueCalledInComposition'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore StateFlowValueCalledInComposition ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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